Gas liquefaction system

Abstract

A gas liquefaction system includes: multiple stages of heat exchangers that cool and liquefy raw material gas to generate liquefied gas by causing the raw material gas to exchange heat with a refrigerant; an expander that decreases a pressure and a temperature of the liquefied gas generated by the multiple stages of heat exchangers by performing adiabatic expansion on the liquefied gas; a magnetic refrigerator that further decreases the temperature of the liquefied gas whose pressure and temperature have been decreased by the expander; a liquefied gas tank that stores the liquefied gas; and a liquid feed line that connects between the magnetic refrigerator and the liquefied gas tank and through which the liquefied gas is fed from the magnetic refrigerator to the liquefied gas tank.

Description

Technical Field

[0001] The present disclosure relates to a gas liquefaction system for liquefying gas.Background Art

[0002] Conventionally, gas liquefaction systems for cooling and liquefying gas, such as natural gas or hydrogen, have been known. Patent Literature 1 discloses a gas liquefaction system of this type.

[0003] Patent Literature 1 discloses a raw material gas liquefier for liquefying raw material gas, such as hydrogen gas. The raw material gas liquefier includes: a feed line through which the raw material gas flows from a raw material gas source to a liquefied gas tank; multiple stages of heat exchangers located on the feed line; and a Joule-Thomson valve located on the feed line. The raw material gas, which is high-pressure gas, is supplied to the feed line. While flowing through the feed line, the raw material gas exchanges heat with a refrigerant at the heat exchanger of each stage, and is thereby cooled in stages to the inversion temperature or lower of the raw material gas. Thereafter, the raw material gas is adiabatically expanded by the Joule-Thomson valve, and consequently turns into a low-temperature normal-pressure liquid that is then fed to the liquefied gas tank.Citation List Patent Literature

[0004] PTL 1: Japanese Laid-Open Patent Application Publication No. 2018-96555Summary of Invention Technical Problem

[0005] While the low-temperature normal-pressure liquefied gas, which is generated by the gas liquefaction system as described above, is being fed to the liquefied gas tank, there is a case where part of the liquefied gas vaporizes due to, for example, heat entering from the outside and pressure loss, and consequently boil off gas is generated. If the boil off gas is generated during the liquefied gas being fed to the liquefied gas tank, it results in a decrease in the raw material gas liquefaction efficiency of the gas liquefaction system.

[0006] The present disclosure has been made in view of the above, and an object of the present disclosure is, in a gas liquefaction system for liquefying raw material gas, to improve the efficiency in liquefying the raw material gas.Solution to Problem

[0007] In order to solve the above-described problems, a gas liquefaction system according to one aspect of the present disclosure includes: multiple stages of heat exchangers that cool and liquefy raw material gas to generate liquefied gas by causing the raw material gas to exchange heat with a refrigerant; an expander that decreases a pressure and a temperature of the liquefied gas generated by the multiple stages of heat exchangers by performing adiabatic expansion on the liquefied gas; a magnetic refrigerator that further decreases the temperature of the liquefied gas whose pressure and temperature have been decreased by the expander; a liquefied gas tank that stores the liquefied gas; and a liquid feed line that connects between the magnetic refrigerator and the liquefied gas tank and through which the liquefied gas is fed from the magnetic refrigerator to the liquefied gas tank.Advantageous Effects of Invention

[0008] The present disclosure makes it possible to, in a gas liquefaction system for liquefying raw material gas, improve the efficiency in liquefying the raw material gas.Brief Description of Drawings

[0009] FIG. 1 is a block diagram showing a schematic configuration of a gas liquefaction system according to one embodiment of the present disclosure. FIG. 2 is a block diagram showing a schematic configuration of a magnetic refrigerator according to one embodiment of the present disclosure. Description of Embodiments

[0010] Next, one embodiment of the present disclosure is described with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a gas liquefaction system 100 according to one embodiment of the present disclosure. The gas liquefaction system 100 according to the present embodiment generates low-temperature normal-pressure liquefied gas by cooling raw material gas. The raw material gas is gaseous at normal temperature and normal pressure, and the boiling point of the raw material gas at normal pressure is lower than the boiling point of nitrogen gas at normal pressure (i.e., lower than -196°C). Examples of such raw material gas include hydrogen gas, helium gas, and neon gas.<<Schematic Configuration of Gas Liquefaction System 100>>

[0011] The gas liquefaction system 100 shown in FIG. 1 includes a feed line 1, through which the raw material gas flows. The feed line 1 includes multiple stages of heat exchangers 7A, 7B, 7C, and 7D, an expander 14, a magnetic refrigerator 2, piping that connects between these elements, etc. The expander 14 is either an expansion turbine that performs adiabatic expansion on the liquefied gas or a Joule-Thomson valve that performs Joule-Thomson expansion on the liquefied gas. The magnetic refrigerator 2 is connected to a liquefied gas tank 94 by a liquid feed line 93.

[0012] The multiple stages of heat exchangers 7A, 7B, 7C, and 7D include an initial-stage heat exchanger 7A, a first middle-stage heat exchanger 7B, a second middle-stage heat exchanger 7C, and a final-stage heat exchanger 7D. Although FIG. 1 shows four stages of heat exchangers 7A, 7B, 7C, and 7D, the number of stages of heat exchangers included in the gas liquefaction system 100 is not limited to four. Further, the multiple stages of heat exchangers 7A, 7B, 7C, and 7D are not limited to the configuration described in the present embodiment, and may be configured differently, so long as the multiple stages of heat exchangers 7A, 7B, 7C, and 7D make it possible to liquefy the raw material gas by cooling the raw material gas in stages.

[0013] In the initial-stage heat exchanger 7A, the raw material gas exchanges heat with a refrigerant in gaseous form and nitrogen gas that is intended for precooling. In the second middle-stage heat exchanger 7C, the raw material gas exchanges heat with the refrigerant in gaseous form. In the present embodiment, hydrogen is used as the refrigerant. However, the refrigerant is not limited to hydrogen, and may be a different substance, so long as the substance is gaseous at normal temperature and normal pressure and has the a boiling point equal to or lower than the boiling point of the raw material gas. Examples of such a refrigerant include hydrogen, helium, and neon.

[0014] The first middle-stage heat exchanger 7B is a liquid nitrogen storage tank that stores liquid nitrogen. The liquid nitrogen storage tank is supplied with the liquid nitrogen. In the first middle-stage heat exchanger 7B, the raw material gas exchanges heat with the refrigerant and the liquid nitrogen, and is thereby cooled to substantially the same temperature as that of the liquid nitrogen. The liquid nitrogen is heated as a result of the heat exchange at the first middle-stage heat exchanger 7B, and consequently vaporizes. The resulting nitrogen gas is fed to the initial-stage heat exchanger 7A, and used for the heat exchange at the initial-stage heat exchanger 7A.

[0015] The final-stage heat exchanger 7D is a liquefied refrigerant storage tank that stores the refrigerant in liquid form. The liquefied refrigerant storage tank is supplied with the refrigerant in liquid form. In the final-stage heat exchanger 7D, the raw material gas exchanges heat with the refrigerant in liquid form, and is thereby cooled to substantially the same temperature as that of the refrigerant in liquid form. Most of the raw material gas that has gone through the heat exchange at the final-stage heat exchanger 7D is liquefied. The refrigerant is heated as a result of the heat exchange at the final-stage heat exchanger 7D, and consequently vaporizes. The vaporized refrigerant is fed to the second middle-stage heat exchanger 7C, and used for the heat exchange at the second middle-stage heat exchanger 7C.

[0016] The refrigerant used in the multiple stages of heat exchangers 7A, 7B, 7C, and 7D is circulated for reuse. The gas liquefaction system 100 includes a refrigerant circulation line 8, through which the refrigerant circulates. The refrigerant circulation line 8 extends through the multiple stages of heat exchangers 7A, 7B, 7C, and 7D, an expansion turbine 81, and a compressor 82. The refrigerant circulation line 8 includes: a forward passage 85 from the compressor 82 to the final-stage heat exchanger 7D; and a return passage 86 from the final-stage heat exchanger 7D to the compressor 82.

[0017] In the forward passage 85 of the refrigerant circulation line 8, the refrigerant fed from the compressor 82 flows in a manner to pass through the initial-stage heat exchanger 7A, the first middle-stage heat exchanger 7B, and the expansion turbine 81 in this order, and reaches the final-stage heat exchanger 7D. The refrigerant that has exited the first middle-stage heat exchanger 7B is liquefied by expansion at the expansion turbine 81, and then flows into the final-stage heat exchanger 7D. Instead of the expansion turbine 81, a Joule-Thomson valve may be used, which liquefies the refrigerant by Joule-Thomson expansion.

[0018] In the return passage 86 of the refrigerant circulation line 8, the refrigerant in gaseous form that has exited the final-stage heat exchanger 7D flows in a manner to pass through the second middle-stage heat exchanger 7C and the initial-stage heat exchanger 7A in this order, and then flows into the compressor 82.<<Method of Liquefaction by Gas Liquefaction System 100>>

[0019] Next, a method of liquefying the raw material gas by the gas liquefaction system 100 configured as above is described. The raw material gas that has a first pressure and a first temperature is supplied from a raw material gas source to the feed line 1. The first pressure is higher than the atmospheric pressure, and is 5 to 10 MPa as a non-limiting example. The first temperature is the normal temperature or a temperature close to the normal temperature.

[0020] The raw material gas that has been supplied to the feed line 1 is cooled in stages by passing through the initial-stage heat exchanger 7A, the first middle-stage heat exchanger 7B, the second middle-stage heat exchanger 7C, and the final-stage heat exchanger 7D in this order, thereby turning into a liquid having the first pressure and a second temperature (i.e., turning into liquefied gas), and flows into the expander 14. The liquefied gas that flows into the expander 14 is not strictly limited to liquid form. Alternatively, the liquefied gas may be a liquid in which gas bubbles are present, i.e., may be a gas-liquid two-phase flow. The second temperature is lower than the first temperature, and is substantially equal to the temperature of the refrigerant in liquid form in the final-stage heat exchanger 7D.

[0021] The liquefied gas that has flowed into the expander 14 and that has the first pressure and the second temperature decreases in pressure and temperature due to adiabatic expansion, and consequently the liquefied gas has a second pressure and a third temperature. The liquefied gas having the second pressure and the third temperature flows out of the expander 14. The second pressure is lower than the first pressure and higher than the atmospheric pressure. The second pressure is not particularly limited, and is, for example, 1.3 to 2 MPa. The second pressure is a pressure compatible with the pressure resistance specifications of the liquefied gas tank 94, and is preferably slightly higher than the normal pressure. The third temperature is lower than the second temperature.

[0022] The liquefied gas that has exited the expander 14 and that has the second pressure and the third temperature flows into the magnetic refrigerator 2, and the liquefied gas further decreases in temperature in the magnetic refrigerator 2. Consequently, the liquefied gas has the second pressure and a fourth temperature. The fourth temperature is lower than the third temperature, higher than the melting point of the liquefied gas having the second pressure, and lower than the boiling point of the liquefied gas having the second pressure. However, the fourth temperature may be lower than the melting point of the liquefied gas having the second pressure, and the liquefied gas may be cooled to a supercooled state by the magnetic refrigerator 2. FIG. 1 shows the magnetic refrigerator 2, which is a single-stage magnetic refrigerator. Alternatively, multiple stages of magnetic refrigerators 2 may be located in series on the feed line 1. In this case, the multiple stages of magnetic refrigerators 2 decrease the temperature of the liquefied gas in stages. The liquefied gas whose temperature has decreased at the magnetic refrigerator 2 is fed to the liquefied gas tank 94 through the liquid feed line 93.<<Configuration of Magnetic Refrigerator 2>>

[0023] Hereinafter, the configuration of the magnetic refrigerator 2 is described in detail. The magnetic refrigerator 2 is located on the feed line 1 at a position downstream of the expander 14. The magnetic refrigerator 2 further cools the liquefied gas that is fed from the expander 14, and discharges the cooled liquefied gas to the liquid feed line 93. The liquefied gas that has flowed out of the magnetic refrigerator 2 into the liquid feed line 93 is fed to the liquefied gas tank 94 through the liquid feed line 93, and is stored in the liquefied gas tank 94. Thus, the liquefied gas that has been cooled to a temperature lower than its boiling point by the magnetic refrigerator 2 flows into the liquid feed line 93. This makes it possible to suppress vaporization of the liquefied gas while it is being fed through the liquid feed line 93. As a result, the efficiency in liquefying the raw material gas increases.

[0024] FIG. 2 is a block diagram showing a schematic configuration of the magnetic refrigerator 2 according to one embodiment of the present disclosure. The magnetic refrigerator 2 shown in FIG. 2 includes: a working vessel 21; a magnetic working material 22 located in the working vessel 21; a magnet 23 located outside the working vessel 21; and a heat transfer medium circulatory passage 50, through which a refrigerant circulates. In the magnetic refrigerator 2, the refrigerant that transfers heat discharged from the magnetic refrigerator 2 is the same substance as the liquefied gas that flows into the magnetic refrigerator 2 from the feed line 1.

[0025] The working vessel 21 includes a refrigeration working chamber 20 filled with the liquefied gas, which serves both as a process fluid and as a heat transfer medium. The working vessel 21 includes a first end 21a and a second end 21b. The second end 21b is located away from the first end 21a. On the first end 21a of the working vessel 21, an inlet 24 and a return inlet 27 are located, each of which is an inlet for the liquefied gas. On the second end 21b of the working vessel 21, a cold outlet 25 and a hot outlet 26 are located, each of which is an outlet for the liquefied gas. In the refrigeration working chamber 20, the liquefied gas flows from the first end 21a toward the second end 21b.

[0026] The magnetic working material 22 is a magnetic material called a magnetocaloric material. The magnetic working material 22 is located in the working vessel 21 between the first end 21a and the second end 21b. That is, the magnetic working material 22 is located within a flow of the liquefied gas in the working vessel 21. The magnetic working material 22 includes passages for the liquefied gas. The form of the magnetic working material 22 is not particularly limited. For example, the magnetic working material 22 is made up of a large number of particles accommodated in a container, and includes passages between the particles, which allow the liquefied gas to pass through.

[0027] The magnet 23 is a magnet to form a magnetic field on the magnetic working material 22, and enables switching between magnetization and demagnetization of the magnetic working material 22. For example, the magnet 23 is a permanent magnet, and moving the magnet 23 relative to the magnetic working material 22 enables switching between magnetization and demagnetization of the magnetic working material 22. As another example, the magnet 23 is an electromagnet, and switching between magnetization and demagnetization of the magnetic working material 22 is enabled by supplying or not supplying an electric current to the electromagnet.

[0028] The feed line 1 is connected to the inlet 24 of the working vessel 21. The liquefied gas flows from the feed line 1 into the refrigeration working chamber 20 of the working vessel 21 through the inlet 24. The liquefied gas supplied to the refrigeration working chamber 20 is not strictly limited to liquid form. Alternatively, the liquefied gas may be a liquid in which a small number of gas bubbles are present, i.e., may be in a gas-liquid two-phase state. A feed valve 32 is located on the feed line 1 at a position downstream of the expander 14 and upstream of the magnetic refrigerator 2. The feed valve 32 is an on-off valve or a flow regulating valve, and the feed valve 32 switches between allowing and blocking communication between the feed line 1 and the working vessel 21. When the feed valve 32 is opened, the liquefied gas is supplied from the feed line 1 to the magnetic refrigerator 2, whereas when the feed valve 32 is closed, the supply of the liquefied gas from the feed line 1 to the magnetic refrigerator 2 is blocked.

[0029] The cold outlet 25 of the working vessel 21 is connected to the liquid feed line 93. During steady-state operation, the liquefied gas whose temperature is lower than the temperature of the liquefied gas that flows into the working vessel 21, i.e., the liquefied gas that has been cooled in the working vessel 21, is discharged to the liquid feed line 93. A cold discharge valve 41 is located on the liquid feed line 93. The cold discharge valve 41 is an on-off valve or a flow regulating valve, and the cold discharge valve 41 switches between allowing and blocking communication between the working vessel 21 and the liquid feed line 93. When the cold discharge valve 41 is opened, the liquefied gas is discharged from the working vessel 21 to the liquid feed line 93, whereas when the cold discharge valve 41 is closed, the discharge of the liquefied gas from the working vessel 21 to the liquid feed line 93 is blocked.

[0030] The hot outlet 26 of the working vessel 21 is connected to a hot discharge line 5. The hot discharge line 5 is configured using piping or the like. During steady-state operation, the liquefied gas whose temperature is higher than the temperature of the liquefied gas that flows into the working vessel 21, i.e., the liquefied gas whose temperature has been increased in the working vessel 21, is discharged to the hot discharge line 5. A hot discharge valve 52 is located on the hot discharge line 5. The hot discharge valve 52 is an on-off valve or a flow regulating valve, and the hot discharge valve 52 switches between allowing or blocking communication between the working vessel 21 and the hot discharge line 5. When the hot discharge valve 52 is opened, the liquefied gas is discharged from the working vessel 21 to the hot discharge line 5, whereas when the hot discharge valve 52 is closed, the discharge of the liquefied gas from the working vessel 21 to the hot discharge line 5 is blocked.

[0031] A cooler 51 is located on the hot discharge line 5 at a position downstream of the hot discharge valve 52. The cooler 51 cools the liquefied gas flowing through the hot discharge line 5. The cooler 51 causes the refrigerant flowing through the refrigerant circulation line 8 and the liquefied gas flowing through the hot discharge line 5 to exchange heat with each other. For example, the cooler 51 causes the refrigerant in liquid form stored in the liquefied refrigerant storage tank, which is the final-stage heat exchanger 7D, and the liquefied gas flowing through the hot discharge line 5 to exchange heat with each other. The cooler 51 is not limited to a particular configuration, and may be configured in any manner, so long as the cooler 51 causes the refrigerant that has been used to exchange heat with the raw material gas in at least one of the multiple stages of heat exchangers 7A, 7B, 7C, and 7D and the liquefied gas flowing through the hot discharge line 5 to exchange heat with each other.

[0032] The liquefied gas that has been cooled by the cooler 51 is fed to a buffer tank 54, and stored in the buffer tank 54. The buffer tank 54 and the return inlet 27 of the working vessel 21 are connected to each other by a return line 6. The liquefied gas stored in the buffer tank 54 is returned to the refrigeration working chamber 20 in the working vessel 21 through the return line 6. The working vessel 21, the hot discharge line 5, and the return line 6 form the heat transfer medium circulatory passage 50, through which the liquefied gas circulates. The liquefied gas circulating through the heat transfer medium circulatory passage 50 functions as a heat transfer medium to transfer heat generated by the magnetic refrigerator 2 to the outside.

[0033] A pump 55 is located on the return line 6. The pump 55 increases the pressure of the liquefied gas stored in the buffer tank 54, and then feeds the liquefied gas to the working vessel 21. A return valve 53 is located on the return line 6 at a position downstream of the pump 55. The return valve 53 is an on-off valve or a flow regulating valve, and the return valve 53 switches between allowing and blocking communication between the return line 6 and the working vessel 21. When the return valve 53 is opened, the liquefied gas is supplied from the return line 6 to the magnetic refrigerator 2, whereas when the return valve 53 is closed, the supply of the liquefied gas from the return line 6 to the magnetic refrigerator 2 is blocked.<<Method of Operating Magnetic Refrigerator 2>>

[0034] The magnetic refrigerator 2 configured as described above first performs initial cooling on the magnetic working material 22 to store cold energy in the magnetic working material 22. In the initial cooling of the magnetic refrigerator 2, a magnetic refrigeration cycle including (a) an adiabatic magnetization step, (b) a heat-discharging magnetization step, (c) an adiabatic demagnetization step, and (d') an initial heat-absorbing demagnetization step is performed at least once, and thereby cold energy is accumulated until a predetermined initial temperature is reached. The initial temperature is an arbitrary temperature that is lower than a target cooling temperature for the liquefied gas (i.e., lower than the aforementioned fourth temperature).(a) Adiabatic Magnetization Step

[0035] The refrigeration working chamber 20 is filled with the liquefied gas in advance. In a state where the feed valve 32, the cold discharge valve 41, the hot discharge valve 52, and the return valve 53 are closed, a magnetic field is externally applied to the magnetic working material 22 by the magnet 23. In this manner, the magnetic working material 22 is magnetized in an adiabatic state, and consequently generates heat.(b) Heat-Discharging Magnetization Step

[0036] From the adiabatic magnetization step, the magnetic working material 22 is continuously magnetized, and the pump 55 is operated in a state where the feed valve 32 and the cold discharge valve 41 are closed and the hot discharge valve 52 and the return valve 53 are opened. As a result of the pump 55 being operated, the liquefied gas stored in the buffer tank 54 is supplied to the working vessel 21 through the return line 6. In the working vessel 21, the magnetic working material 22 and the liquefied gas exchange heat with each other, and the magnetic working material 22 releases heat to the liquefied gas. The liquefied gas whose temperature has increased due to the heat is discharged from the hot outlet 26 to the hot discharge line 5.(c) Adiabatic Demagnetization Step

[0037] In a state where the feed valve 32, the cold discharge valve 41, the hot discharge valve 52, and the return valve 53 are closed, the intensity of the magnetic field applied to the magnetic working material 22 by the magnet 23 is reduced. In this manner, the magnet 23 is demagnetized in an adiabatic state, and consequently absorbs heat from the surroundings.(d') Initial Heat-Absorbing Demagnetization Step

[0038] From the adiabatic demagnetization step, the magnetic working material 22 is continuously demagnetized, and the pump 55 is operated in a state where the feed valve 32 and the cold discharge valve 41 are closed and the hot discharge valve 52 and the return valve 53 are opened. As a result of the pump 55 being operated, the liquefied gas stored in the buffer tank 54 is supplied to the working vessel 21 through the return line 6. In the working vessel 21, the magnetic working material 22 and the liquefied gas exchange heat with each other, and the magnetic working material 22 absorbs heat from the liquefied gas. The liquefied gas whose temperature has decreased as a result of the heat of the liquefied gas being absorbed by the magnetic working material 22 is discharged from the hot outlet 26 to the hot discharge line 5.

[0039] When the initial cooling of the magnetic refrigerator 2 has ended, steady-state operation is started. During the steady-state operation, the magnetic refrigerator 2 performs a magnetic refrigeration cycle including (a) the adiabatic magnetization step, (b) the heat-discharging magnetization step, (c) the adiabatic demagnetization step, and (d) a heat-absorbing demagnetization step, thereby supercooling the liquefied gas supplied from the feed line 1, and discharges the supercooled liquefied gas to the liquid feed line 93. The only difference between the magnetic refrigeration cycle during the steady-state operation and the magnetic refrigeration cycle during the initial cooling lies in (d) the heat-absorbing demagnetization step. Therefore, hereinafter, (d) the heat-absorbing demagnetization step will be described in detail, and the detailed description of the other steps will be omitted below.(d) Heat-Absorbing Demagnetization Step

[0040] In a state where the magnetic working material 22 is demagnetized continuously from the adiabatic demagnetization step, the hot discharge valve 52 and the return valve 53 are closed, and the feed valve 32 and the cold discharge valve 41 are opened. The liquefied gas is supplied to the working vessel 21 through the feed line 1. In the working vessel 21, the magnetic working material 22 and the liquefied gas exchange heat with each other, and the magnetic working material 22 absorbs heat from the liquefied gas. The liquefied gas whose temperature has decreased as a result of the heat of the liquefied gas being absorbed by the magnetic working material 22 is discharged from the cold outlet 25 to the liquid feed line 93.[Summary]

[0041] A gas liquefaction system 100 according to item 1 of the present disclosure includes: multiple stages of heat exchangers 7A, 7B, 7C, and 7D, which cool and liquefy raw material gas to generate liquefied gas by causing the raw material gas to exchange heat with a refrigerant; an expander 14, which decreases a pressure and a temperature of the liquefied gas generated by the multiple stages of heat exchangers 7A, 7B, 7C, and 7D by performing adiabatic expansion on the liquefied gas; a magnetic refrigerator 2, which further decreases the temperature of the liquefied gas whose pressure and temperature have been decreased by the expander 14; a liquefied gas tank 94, which stores the liquefied gas; and a liquid feed line 93, which connects between the magnetic refrigerator 2 and the liquefied gas tank 94 and through which the liquefied gas is fed from the magnetic refrigerator 2 to the liquefied gas tank 94.

[0042] In the gas liquefaction system 100 configured as described above, the liquefied gas that has decreased in pressure and temperature at the expander 14 further decreases in temperature at the magnetic refrigerator 2, and consequently, the liquefied gas has a temperature lower than its boiling point. While being fed through the liquid feed line 93, although the liquefied gas receives heat entering from the outside and decreases in pressure due to pressure loss, vaporization of the liquefied gas is suppressed. As a result of the vaporization of the liquefied gas being suppressed during the feeding of the liquefied gas, the proportion of the mass of the liquefied gas generated from the raw material gas and then stored in the liquefied gas tank 94 to the mass of the raw material gas supplied to the gas liquefaction system 100, i.e., the efficiency in liquefying the raw material gas, increases.

[0043] The gas liquefaction system 100 according to item 2 of the present disclosure is configure such that, in the gas liquefaction system 100 according to item 1, the magnetic refrigerator 2 includes: a working vessel 21, which is filled with a heat transfer medium in liquid form; a magnetic working material 22, which is located in the working vessel 21; a magnet 23, which is located outside the working vessel 21 and which enables magnetization and demagnetization of the magnetic working material 22; a cooler 51, which cools the heat transfer medium by causing the heat transfer medium to exchange heat with the refrigerant; and a heat transfer medium circulatory passage 50, through which the heat transfer medium circulates in a manner to pass through the working vessel 21 and the cooler 51.

[0044] In the gas liquefaction system 100 configured as described above, the heat transfer medium of the magnetic refrigerator 2 is cooled by using the refrigerant that cools the raw material gas at the heat exchangers 7A, 7B, 7C, and 7D. In this manner, cold energy within the system is utilized efficiently.

[0045] The gas liquefaction system 100 according to item 3 of the present disclosure is configured such that, in the gas liquefaction system 100 according to item 2, among the multiple stages of heat exchangers 7A, 7B, 7C, and 7D, a final-stage heat exchanger 7D, through which the raw material gas passes last is a liquid storage tank that stores the refrigerant in liquid form that is used to exchange heat with the raw material gas, and the cooler 51 causes the heat transfer medium and part of the refrigerant in liquid form stored in the liquid storage tank to exchange heat with each other.

[0046] The magnetic refrigerator 2 configured as described above causes the heat transfer medium to exchange heat with the refrigerant in liquid form. This makes it possible to cool the heat transfer medium efficiently.

[0047] The gas liquefaction system 100 according to item 4 of the present disclosure is configured such that, in the gas liquefaction system 100 according to item 2 or 3, the heat transfer medium and the liquefied gas are the same substance, and the magnetic refrigerator 2: causes, by adiabatic magnetization, the magnetic working material 22 to generate heat; supplies the heat transfer medium in liquid form to the working vessel 21, and discharges the heat transfer medium whose temperature has increased due to the heat generated by the magnetic working material 22 to the heat transfer medium circulatory passage; causes, by adiabatic demagnetization, the magnetic working material 22 to absorb heat; and supplies the liquefied gas to the working vessel 21, and discharges the liquefied gas whose temperature has decreased as a result of heat of the liquefied gas being absorbed by the magnetic working material 22 to the liquid feed line 93.

[0048] In the gas liquefaction system 100 configured as described above, in the magnetic refrigerator 2, the magnetic working material 22 and the liquefied gas directly exchange heat with each other, and thereby the liquefied gas is cooled. Therefore, the liquefied gas can be cooled with higher efficiency than in a case where the liquefied gas indirectly exchanges heat with the magnetic working material 22.

[0049] The present disclosure has been discussed as above for the purpose of presenting examples and explanations, and the above discussion has no intention to limit the present disclosure to the modes disclosed herein. For example, in the above detailed description, various features of the present disclosure are grouped together in one embodiment for the purpose of streamlining the present disclosure. However, some of the features therein may be combined together. Further, the features included in the present disclosure may be combined with alternative embodiments, alternative configurations, or alternatively modes, other than those described above.

Claims

1. A gas liquefaction system comprising: multiple stages of heat exchangers that cool and liquefy raw material gas to generate liquefied gas by causing the raw material gas to exchange heat with a refrigerant; an expander that decreases a pressure and a temperature of the liquefied gas generated by the multiple stages of heat exchangers by performing adiabatic expansion on the liquefied gas; a magnetic refrigerator that further decreases the temperature of the liquefied gas whose pressure and temperature have been decreased by the expander; a liquefied gas tank that stores the liquefied gas; and a liquid feed line that connects between the magnetic refrigerator and the liquefied gas tank and through which the liquefied gas is fed from the magnetic refrigerator to the liquefied gas tank.

2. The gas liquefaction system according to claim 1, wherein the magnetic refrigerator includes: a working vessel that is filled with a heat transfer medium in liquid form; a magnetic working material that is located in the working vessel; a magnet that is located outside the working vessel and that enables magnetization and demagnetization of the magnetic working material; a cooler that cools the heat transfer medium by causing the heat transfer medium to exchange heat with the refrigerant; and a heat transfer medium circulatory passage through which the heat transfer medium circulates in a manner to pass through the working vessel and the cooler.

3. The gas liquefaction system according to claim 2, wherein among the multiple stages of heat exchangers, a final-stage heat exchanger through which the raw material gas passes last is a liquid storage tank that stores the refrigerant in liquid form that is used to exchange heat with the raw material gas, and the cooler causes the heat transfer medium and part of the refrigerant in liquid form stored in the liquid storage tank to exchange heat with each other.

4. The gas liquefaction system according to claim 2 or 3, wherein the heat transfer medium and the liquefied gas are the same substance, and the magnetic refrigerator: causes, by adiabatic magnetization, the magnetic working material to generate heat; supplies the heat transfer medium in liquid form to the working vessel, and discharges the heat transfer medium whose temperature has increased due to the heat generated by the magnetic working material to the heat transfer medium circulatory passage; causes, by adiabatic demagnetization, the magnetic working material to absorb heat; and supplies the liquefied gas to the working vessel, and discharges the liquefied gas whose temperature has decreased as a result of heat of the liquefied gas being absorbed by the magnetic working material to the liquid feed line.

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